jcb 3cx problem

[Bear21]

hi, I own a 1983 model 3cx which is a great machine apart from one annoying problem which I am looking for suggestions on what the problem is...... the back actor keeps dropping under its own weight! all ram seals have been replaced and there is no oil leaking from anywhere! when this problem first started it was only now and again,now its all the time which makes me think that it might have something to do with a valve sticking in the control block or maybe a seal gone inside it?? but I am not a mechanic! any suggestions will be much appreciated! cheers

 

[newty]

Hi,

The control valve would be the next place to look for scoring and general wear. How long does it take to drop?

 

[Bear21]

Hi
well when the machine is cold it not to bad but as soon as the oil warms up its dropping fairly quick. if you look the back actor in place to stop it dropping when not in use either the extending dipper will start to slowly creep out or the bucket crowd will start to go!is there a valve which could be sticking open where the main feed goes in or out of the control block or maybe seals?? this problem used to be only now and again but now its constant! cheers

 

[Anto Modded]

I doubt its an inner seal in a ram as you said the extra did or bucket can also drop. Is there any leaks in the hydrauilic system. We had a 94 sitemaster and it used to drop the extra dig and one jack leg when driving on the road. The valve chest was pissing fluid as someone tried to clean the dirt and scorned the valves as seals didnt stop it. we sold it after as it was a machine that always gave trouble

 

[willie59]

Does that 3CX have linkage controls or pilot operated joystick controls?

 

[Bear21]

This 3cx has linkage controls

 

[Bear21]

hi anto modded no there is no leaks anywhere in the hydrualic system,and we have replaced all the seals on all the rams on the back actor about 6 months ago, all this said I am still thinking it something to do with the vavlve chest, we changed the hydrualic oil recently so maybe disturbed dirt and it has got into the valve chest and causing a valve to not shut fully. is stipping the valve chest a big job? its becoming a right pain in the arse having to lock the back actor up all the time when not in use!!

 

[willie59]

Bear21, I'm looking over the schematics for your machine and if it's a gear pump machine with linkage controls, I don't see anything that would cause this problem because the valves are open center and the work ports (A & B) are blocked when valve is centered.

However, if it's a variable displacement pump with linkage controls, if it were to have a blockage in the tank return line from hoe control valve, the anti-cavitation valves for boom and dipper extend would cause them to drop. But, unless the schematic has an error (have seen it before), there's no anti-cavitation valve shown in the circuit for bucket crowd or extend, which would seem odd to me if they were, in fact, not there.

Another possibility would be the caps on the centering springs for valve sections are loose causing spools to not be centered. Would be unusual for three different caps to be loose, but something worth looking at.

I just can't see anything else from viewing schematic that would cause this problem on three different functions.

 

[Bear21]

willie59, Thanks alot for that, that has been a huge help,will check out all these possibilitys and hopefully get rid of this problem.cheers!

 

[willie59]

willie59, Thanks alot for that, that has been a huge help,will check out all these possibilitys and hopefully get rid of this problem.cheers!

Well, I'm still not certain at what you're problem is Bear21, just throwing some ideas out there. Let us know if you discover any other tidbit of info that might give a clue as to the cause.

 

[Anto Modded]

Could it be an inner seal in the ram for the boom and the extra dig. I had a thread up a while back where my minidigger had dirt in the system and it would start tracking when using the bucket. Turned out to be dirt in the system, so i canged the filter in the tank and worked it for a while and changed it again a few weeks after with new oil again and it be working over a year now with no problems. I would think inner seals maybe or valve chest. ine thing you might be able to try is switching the hoses at the valvechest and see if the boom holds up, or get 2 long lengths of hose and switch from the connections on the ram itself maybe, you will eventually find the problem and its usually something simple in the end

 

[Bear21]

Could it be an inner seal in the ram for the boom and the extra dig. I had a thread up a while back where my minidigger had dirt in the system and it would start tracking when using the bucket. Turned out to be dirt in the system, so i canged the filter in the tank and worked it for a while and changed it again a few weeks after with new oil again and it be working over a year now with no problems. I would think inner seals maybe or valve chest. ine thing you might be able to try is switching the hoses at the valvechest and see if the boom holds up, or get 2 long lengths of hose and switch from the connections on the ram itself maybe, you will eventually find the problem and its usually something simple in the end

well now that you mentioned that the hydrualic filter and oil was replaced not long before this problem started and going by the condition of the old filter it looked like the original one!!!! when the filter was removed there was nothing left of it! and bits of it missing! i guess its just a case of trying to find the missing bits now!! hope to get somthing done on the machine over the next couple weeks will try all these suggestions and hopefully get to the bottom of it!! cheers